When the interrogative pronouns is the subject of the sentence, the worm who is used.
Examples of Interrogative Pronouns as the subject of the sentence
Who is that woman?
Who came first this morning?
Who have money for drinks?
Who fancy a pint of beer?

Interrogative Pronouns – Who?
As can be seen from the given examples, in these sentences the affirmative verb forms are used.
When this pronouns is used in the function of an object, the form whom is used:
Examples of – Whom
Whom did you ask?
Whom did you saw?
Whom do you want?
Whom does she knows there?
When this pronoun is used with a preposition, two constructions are possible. :proposition + whom or who … proposition. The form whom may be used with a preposition preceding it or the form who with the preposition at the end of the sentence if there is not an adverbial requiring the final position.
Examples of Interrogative Pronouns – Who
preposition + whom | who … proposition |
---|---|
For whom are you buying that? | Who are you waiting for? |
With whom will she go today? | Who will she go with today? |
Of whom are you talking? | Who are you talking of? |
To whom did you give the beer? | Who did you give the beer to? |